Paper industry continuously strives to improve paper and paperboard quality, increase process speeds, reduce manufacturing costs etc. Various chemicals, synthetic and naturally occurring, are used to treat pulp in order to improve, for example, retention, fixing and drainage, and to create physical properties such as wet and dry strength of the final paper product. Typically synthetic chemicals, synthetic polymers, are tailored for one purpose, for example either for giving strength or drainage properties.
A retention agent is a process chemical that improves retention of a functional chemical in a substrate. The result is that totally fewer chemicals are used to get the same effect of the functional chemical and fewer chemicals goes to waste.
Drainage additives are materials that increase drainage rate of water from pulp slurry on a wire. Common drainage additives are cationic starch and polyacrylamide.
Wet strength additives ensure that when paper becomes wet, it retains its strength. This is especially important in a tissue paper. Examples of wet strength additives are urea-formaldehyde (UF), melamine-formaldehyde (MF) and polyamidoamide-epichlorohydrin (PAE).
Dry strength additives are chemicals that improve paper strength of normal or not wet condition. Typical chemicals used are starch and polyacrylamide (PAM) derivatives. The starch and PAM derivatives may be anionically or cationically charged. By using cationic starch or PAM, negatively charged fibers can bind with the cationic starch or PAM and thus increase interconnections between the fibers, and thus strength.
For example, U.S. Pat. No. 4,421,602 discloses use of partially hydrolyzed homopolymers of N-vinylformamide as retention and drainage aid and flocculant in papermaking. EP 438707 discloses use of hydrolyzed homo- or copolymers of N-vinylformamide as fixing agent in papermaking.
US 2008/0000601 A1 discloses a process for production of paper, board and cardboard by draining a paper stock on a wire in the presence of at least one polymer as retention aid with sheet formation and drying of the sheets, wherein the sheet formation is carried out in absence of inorganic flocculants, and (a) polymers comprising vinylamine units and/or polyvinylformamide, and (b) at least one cationic or nonionic polyacrylamide and/or one cationic or nonionic polymethacrylamide are used as retention aids.
An Interpenetrating Polymer Network (IPN) is a material with a network of at least two polymers which are at least partially interlaced on a molecular scale. The polymers cannot be separated unless chemical bonds are broken. The polymers can be envisioned to be entangled in such a way that they are concatenated and cannot be pulled apart, but substantially unbonded to each other by chemical bonds. In other words, the interpenetrating polymer networks are a combination of at least two polymers, wherein at least one of the polymers is synthesized (polymerized) and/or cross-linked in the immediate presence of the other(s).
Simply mixing two or more polymers does not create an interpenetrating polymer network but a polymer blend, nor does creating a polymer network out of at least one kind of monomer(s) which are bonded to each other to form one network (heteropolymer or copolymer).
For example, CN104311841 relates to a method for preparing an interpenetrating polymer network. The method comprises the following steps: mixing acrylamide and sodium alginate, adding a cross-linking agent and an initiator, performing polymerization of acrylamide, forming a polyacrylamide gel network with sodium alginate.
Even though there are available IPN materials, there is still a need for novel IPN materials to be used as additives in production of paper and paperboard having improved properties.